Characterization of electron beam irradiation blends based on metallocene ethylene-1-octene copolymer

Characterization of Electron Beam Irradiation BlendsBased on Metallocene Ethylene-1-Octene Copolymer

MIGUEL ANGEL CARDENAS,1,2 NORKY VILLARREAL,1 ISABEL GOBERNADO-MITRE,1

JUAN CARLOS MERINO,1,2 JOSE MARIA PASTOR1,2

1CIDAUT (Foundation for Research and Development in Transport and Energy),Parque Tecnologico de Boecillo P.209, 47151 Boecillo, Valladolid, Spain

2Dpto. Fısica de la Materia Condensada, E.T.S.I.I. Universidad de Valladolid,Po. del Cauce s/n, 47011 Valladolid, Spain

Received 7 February 2007; revised 23 May 2007; accepted 29 May 2007DOI: 10.1002/polb.21259Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: Binary blends using metallocene ethylene-1-octene copolymer as matrixwere prepared and subjected to electron beam (EB) irradiation (50, 100, and200 kGy). Gel content and melt flow index values indicated that the blends werecrosslinking. Fourier transform infrared-ATR spectroscopy was used to study thecrosslinking and oxidative degradation of the blends via tertiary carbon and carboxylgroup formation, respectively. Thermal and mechanical properties were studied show-ing that the crystallinity of both matrix and dispersed phase decreased with irradia-tion dose, and that the thermoplastic elastomers with good mechanical propertiesmay be obtained by EB irradiation. Chain branching and scission were also detectedat all irradiation doses, although at the highest doses (200 kGy) a crosslinking reac-tion was the most predominantly observed effect. The successive self-nucleationannealing technique was used to determine the EB irradiation effects on crystalliza-tion of some blends in which crosslinking and chain branching take place, modifyingthe chain’s structure and therefore crystalline regions in the matrix and the dis-persed phase. VVC 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2432–2440,

2007

Keywords: blends; crosslinking; FTIR; irradiation; successive self-nucleationannealing

INTRODUCTION

The development of metallocene catalysts in thefield of polyolefins permits the production of newethylene copolymers with very low density thatconstitute an unique class of thermoplastic elas-tomers.1,2 These polymers are special because oftheir regular structure and homogeneous como-nomer distribution, and their promising mechan-

ical properties open the door to a wide range ofapplications.3 However, owing to the molecularcharacteristics of metallocene polyethylene (mPE),its potential market is limited because of poorprocessability. Blends of polyolefins have beenextensively studied to obtain new materials withimproved properties, and in many cases, blend-ing is the simplest and the best way to make thisimprovement.4–8

To achieve a good balance in their propertiesat high temperatures, mPE and even their blendshave been subjected to crosslinking reactionsby irradiation.9–11 Many research works havefocused on the effects of irradiation on thermal,

Correspondence to: J. M. Pastor (E-mail: [email protected])

Journal of Polymer Science: Part B: Polymer Physics, Vol. 45, 2432–2440 (2007)VVC 2007 Wiley Periodicals, Inc.

2432

morphological, and mechanical behavior of re-cycled conventional polyethylene blends,12–16 andon the properties of polypropylene (PP) blends.17,18

This article presents the characterization of anew material obtained by the irradiation ofblends of ethylene-1-octene metallocene copoly-mer with a high density polyethylene (HDPE), alinear low-density polyethylene (LLDPE), and aPP.

Polymers can be crosslinked by irradiation orchemical processes. Irradiation takes place in thesolid state and by means of chemical methods inthe molten state; both methods yield carbon–car-bon crosslinks. Irradiation is a very powerfulform of energy treatment and produces deepeffects on materials. Two of the most commonindustrial irradiation types used are gamma irra-diation (c) and electron beam (EB) irradiation.EB irradiation has limited penetration comparedwith gamma-rays; however, it is very energy-effi-cient because the entire amount of energy is de-posited on the sample. As EB irradiation containsno radioactive isotope, it provides a significantadvantage from a public acceptance point ofview.19

The chemical effects of exposing a polymericmaterial to EB irradiation can be likened to thephenomenon of ionization, of which the mostprominent effect is crosslinking. Other chemicalchanges resulting from the exposure to irradia-tion include chain scission, formation of vinyleneunsaturation, conjugated double bonds, andchain branching.20 The advantage of the cross-linking process is based on the changes in poly-mer thermoplastic behavior. Some of the modifi-cations include an increase in dimensional stabil-ity, tensile strength and stress cracking, higherdeformation, resistance to solvents, and abrasion.Chain branching occurs when a hydrogen atom isreplaced by a covalently bonded chain; thismakes the polymers less crystalline and resultsin low tensile strength and melting point. Inchain-scission reactions, the carbon–carbon linksare broken and the resulting radicals tend torelink with hydrogen or oxygen atoms to formshorter polymer chains.

The unique molecular structure of mPE has astrong influence on the efficiency of the crosslink-ing process, because the metallocene catalystdetermines the crystalline degree of the polymer.EB irradiation at a temperature below the melt-ing point of the polymer allows a crosslinking for-mation in the amorphous part of the material.However, other radicals formed during the irradi-

ation process can remain trapped in its crystal-line phases. Thus, the amounts of both amor-phous and crystalline phases play an importantrole during the crosslinking process.

In this work, we applied EB irradiation as acrosslinking method for blends to obtain a deepcompatibilization between their components andto improve properties such as tensile strength,stress cracking, deformation, and resistance totemperature. To this end, mechanical and ther-mal properties were evaluated. We also investi-gated the effects of three different EB irradiationdoses on the molecular structure of blends usingFourier transform infrared (FTIR) spectroscopyand successive self-nucleation annealing (SSA)technique.

EXPERIMENTAL

Materials

The ethylene-1-octene copolymers used wereEngage 8411 (mPE1) and Engage 8403 (mPE2),manufactured by DuPont-Dow Elastomers basedon the Insite Technology (metallocene catalysts).HDPE and LLDPE synthesized with Ziegler-Natta catalytic were produced by PoliolefinasIndustriales C.A. and Resinas Lineales ResilinC.A., respectively. The isotactic PP used was aStamylan P 17M10 obtained from DSM. In Ta-ble 1 some technical specifications of the poly-mers used are presented.

Processing

The selected blends were prepared in a BerstorffECS (2E25) corotating twin-screw extruder inan 80/20 wt % (Table 2) and a screw speed of100 rpm. Sheets of the blends were molded usingSchwabenthan Polystat 200T hydraulic presscompression molding.

Compressed molded samples were irradiatedin air at room temperature by an EB accelerator(model Rhodotron TT200, 10 MeV) at IONMEDEsterilizacion, S.A. (Tarancon, Spain). The irra-diation process was developed in accumulativesingle exposures of 50 kGy to avoid excessiveheat generation in the samples, for example, theEB irradiation doses of 50, 100, and 200 kGywere obtained by one, two, and four exposures ofthe blends to the beam, respectively.

ELECTRON BEAM IRRADIATION 2433

Journal of Polymer Science: Part B: Polymer PhysicsDOI 10.1002/polb

Characterization

The crosslinking degree is estimated by meansof the gel content as the amount (in wt %) of in-soluble material in boiling xylene accordingto ASTM D2765-95 standard. Melt flow index(MFI) determination was carried out in a CEASTMFI model 7026. The tests were performedaccording to ASTM D1238-90b at 190 8C and2.16 kg for the samples irradiated at 0, 50, and100 kGy.

The mechanical properties were evaluatedwith a Minimat Polymer Laboratories Tensilemachine at room temperature and at 10 mm/min.The dumbbells used were 2-mm thick. An FTIRspectrometer was used to study the molecularchanges induced by EB irradiation in the blends.FTIR analysis was carried out in a Bomem (Hart-mann and Braun) Model NB-150 mounted on aGolden Gate ATR accessory, using 4-cm�1 resolu-tion and 64 scans.

Differential scanning calorimetry (DSC) ther-mograms were recorded on Mettler Toledo DSC-821 equipment at a heating rate of 10 8C/min.The melting behavior analyzed was from a sec-ond scan obtained after erasing the thermal his-tory of the samples. The crystallinities of matrixand dispersed phase were determined accordingto eq 1, where DHm is the melting enthalpy, F isthe weight fraction in the blend, and the DHm

* isthe melting enthalpy of the polymer at 100%

crystallization (DHm* ¼ 290 J/g for polyethylene

and DHm* ¼ 190 J/g for PP).21

Xc ¼ DHm

/DH�m

3100% ð1Þ

The SSA technique consists of successive heatingand cooling cycles.22 In this study, all cycles werecarried out at 10 8C/min. First, each sample washeated and kept in the melt for 5 min to erasethe previous thermal history. Then, it was cooleddown to �40 8C at 10 8C/min creating an initialstandard thermal history. Another heating scanwas carried out at the same rate to a selectedself-seeding temperature denoted Ts, where thesample was kept for 5 min before cooling it downagain to �40 8C at the same rate. The Ts was cho-sen so that the polymer would only self-nucleate,as explained by Muller and Arnal.23 Ts should behigh enough to melt all the crystalline regions,except for small crystal fragments and/or nucleithat can later self-seed the polymer during cool-ing.23,24 After this step, the sample was heatedonce again to a temperature of 5 8C below Ts andheld there for 5 min. Hence, the unmelted crys-tals at this temperature should anneal, and someof the melted species should isothermally crystal-lize during the subsequent cooling. This cyclicprocedure is repeated by heating the sample to atemperature 5 8C lower than that of the previousannealing, until a temperature close to �40 8C is

Table 1. Technical Specifications of the Used Polymers

Polymer NameComonomer

Content (wt %)Density(g/cm3)

MFI(dg/min) Tm (8C) Tc (8C)

mPE1 Engage 8411 33 0.880 18.0 78 55mPE2 Engage 8403 16 0.913 30.0 110 91HDPE Altaven 2100J – 0.957 6.5 128 118LLDPE Resilin X-13 – 0.931 4.6 120 112PP Stamylan 17M10 – 0.905 10.5 168 109

Table 2. Composition of the Blends and Compounding Temperature Profile

Composition (80/20)

Temperature Profile (8C)

T1 T2 T3 T4 T5 T6 T7 Die

mPE1/mPE2 85 150 150 150 150 130 105 105mPE1/HDPE 165 180 180 180 180 150 140 140mPE1/LLDPE 135 160 160 160 160 135 115 115mPE1/PP 170 185 185 185 185 170 160 155

2434 CARDENAS ET AL.


reached. The melting behavior of samples pre-pared was recorded at a heating rate of 10 8C/min.

RESULTS AND DISCUSSION

Gel Content and MFI

The gel content (crosslinking degree) and MFI ofthe irradiated samples as a function of EB irradi-ation doses are shown in Table 3. MFI was usedto observe the ability of the irradiated materialsto flow. The combination of gel content and MFImeasurements provides us with a way to under-stand the reactions involved in the irradiationprocess.

The irradiated material at 200 kGy does notflow through the capillary of the equipment and,therefore, MFI values for this irradiation cannotbe obtained. At 50 and 100 kGy a slight increasein the gel content was observed for all samples,and simultaneously a decrease in their MFI val-ues, more than 60% compared with the blendswithout irradiation was pointed out.

The low-molecular-weight structures formedas a product of chain-scission and chain-branch-ing reactions could be dissolved, meaning thatthey would not contribute to the measured value

during the gel content test. Whilst in the MFItest, both crosslinking and noncrosslinking struc-tures remain inside the blend morphology.

Generally, an increase in the crosslinkingdegree is associated with a decrease in the solu-bility (increase in gel content) and a noticeabledecrease in the flow capacity of the material(MFI decrease). These changes are due to athree-dimensional network formed by the cross-linking process, which acts as a hindrance to theflow of the chains.

Mechanical Properties

The values of the Young’s modulus and the stressat 100% (r100%) and 250% (r250%) of elongationfor the blends irradiated at different doses arepresented in Table 4. Stress and elongation atbreak are not shown because of the fact thatthese were not achieved during the tests. In allEB irradiated blends the modulus values aregreater than the nonirradiated blends. The cross-linking reactions that occurred in our blends sub-jected to EB irradiation were a result of randomevents that lead up to the formation of a three-dimensional network structure. This type ofstructure affects the elastic modulus of the mate-rials. The crosslinked mPE1/mPE2, mPE1/HDPE, and mPE1/LLDPE blends showed highermodulus values, because the crosslinking bondsdisturb the alignment of polyethylene chains.The new links are located in the amorphous andinterface regions.25 Therefore, the crosslinkingdensity in these zones increases considerably asirradiation doses are increased and reinforce-ment takes place in the irradiated blends. Thisreinforcement causes an increase in the modulusof the blends, because the new links (chemical)formed during the irradiation process are addedto the old physical links (crystal) already exist-ing.

In addition, the r100% and r250% values de-creased slightly with the irradiation doses, andwith the higher doses (100 and 200 kGy) a tend-ency to stabilize was observed. These results aresignificant to the maintenance of the elastomericbehavior of the blends. However, the changes inthe mechanical properties evaluated the evidencethat crosslinking is the predominant reaction.26

Fourier Transform Infrared

The irradiation of polymers is known for indu-ced crosslinking, chain-branching, unsaturation,

Table 3. Gel Content and Melt Flow Index (MFI)Values of the Blends

Blend

EBIrradiationDose (kGy)

GelContent

(%)MFI

(dg/min)

mPE1/mPE2 0 0 1850 3 7

100 4 vl200 70 –

mPE1/HDPE 0 0 1450 2 4

100 8 vl200 71 –

mPE1/LLDPE 0 0 1250 3 3

100 7 vl200 74 –

mPE1/PP 0 0 1550 4 6

100 4 vl200 68 –

vl, very low; between 0.1 and 0.9 g/10 min.



chain-scission reactions, and degradation proc-esses. The crosslinking promoted by high energyradiation was studied by infrared spectroscopy,and it was calculated by the area ratio betweenabsorption band of C��H deformation in tertiarycarbons (1320–1360 cm�1) and the absorptionband at 721 cm�1, which corresponds to the CH2

rocking (eq 2).27 To evaluate the possible oxida-tive degradation induced by EB irradiation, thearea ratios between stretching of carbonyl group(C¼¼O) adsorption band at 1705–1740 cm�1 andabsorption band at 721 cm�1 were calculated(eq 3). CH2 rocking absorption band (721 cm�1) ischaracteristic at polyethylene and was used asreference band.27

A1 ¼ Að1320� 1360 cm�1ÞAð721 cm�1Þ ð2Þ

A2 ¼ Að1705� 1740 cm�1ÞAð721 cm�1Þ ð3Þ

FTIR analysis was carried out to confirm theobservations derived from the analysis of gelcontent, MFI, and mechanical properties. In lin-ear polyethylenes (HDPE and LLDPE), themechanism of crosslinking involves the loss oftwo hydrogen atoms and the bonding of the twocarbon-centered free radical sites.27 Thus, terti-ary carbons are generated in the crosslinkingpoints (Fig. 1).26

In Figure 2, the increase in A1 (tertiary car-bon) ratio as a function of EB irradiation dose ispresented. The presence of tertiary carbonsincreases, especially for mPE1/HDPE and mPE1/LLDPE blends, which was expected. The spatialnetwork in crosslinking polymers supposes ahigher amount of tertiary carbons than noncross-linking polymers. In addition, the tertiary carbonincrease can also be a consequence of the pres-ence of chain branching, because their formationmechanism is similar to the crosslinking mecha-nism. In general, all blends have shown chemicalchanges in the chain structures and a predomi-

Figure 1. Crosslinking reaction for polyethylenes.

Table 4. Mechanical Properties of the Blends at Different EB Irradiation Doses

0 (kGy) 50 (kGy) 100 (kGy) 250 (kGy)

mPE1/mPE2E (MPa) 6 0.1 2.7 3.8 3.3 3.3r100% (MPa) 6 0.01 0.50 0.41 0.39 0.37r250% (MPa) 6 0.01 0.57 0.48 0.51 0.51

mPE1/HDPEE (MPa) 6 0.1 4.6 6.8 5.5 5.4r100% (MPa) 6 0.01 0.53 0.51 0.45 0.41r250% (MPa) 6 0.01 0.60 0.63 0.58 0.53

mPE1/LLDPEE (MPa) 6 0.1 3.4 4.2 4.1 4.1r100% (MPa) 6 0.01 0.59 0.46 0.48 0.40r250% (MPa) 6 0.01 0.67 0.57 0.61 0.56

mPE1/PPE (MPa) 6 0.01 2.2 2.9 2.6 2.5r100% (MPa) 6 0.01 0.56 0.49 0.46 0.46r250% (MPa) 6 0.01 0.65 0.63 0.60 0.63



nance of crosslinking (and chain branching) reac-tions over chain-scission reactions.

The progress of the irradiation-induced oxida-tion of polymers depends on the irradiation con-ditions, such as the atmosphere, pressure, doserate, temperature, and the sample dimensions.In Figure 3, the A2 (carbonyl groups) ratio ver-sus the irradiation dose are presented. Theappearance of carbonyl groups increases only at200 kGy for the EB irradiation blends where theradicals formation is greater, thus providing thepossibility of oxidative reactions.26,28

The highest rates of oxidative degradation areto be found in mPE1/HDPE and mPE1/LLDPEblends. The results achieved in the mPE1/PPblend were different from those we expected.This blend should have been more degraded thanit was due to the well-known oxidative behaviorof PP in air. Nevertheless, these results haveallowed us to conclude that the dispersed phasesmost affected by the EB irradiation were theHDPE and the LLDPE. However, it is importantto note that the values of the A2 ratio are verylow, indicating that the chain-scission reactionoccurs less frequently and the effects of the cross-linking and/or chain-branching reactions pre-dominate in all EB-irradiated blends.

Differential Scanning Calorimetry

The values of melting temperature peak (Tm) andcrystallinity degree (Xc) of the matrix (subscripts1) and disperse phase (subscripts 2) after differ-ent EB irradiation doses are summarized inTable 5. The existence of two melting points that

correspond to those of the individual componentsindicated that all the blends are immiscible inthe crystalline regions. Melting temperatures ofthe EB irradiated blends were very close to melt-ing temperatures of the blends without irradia-tion. However, Xc values shift toward lower val-ues, especially for 200 kGy, because of the newchemical links formed in the amorphous phaseduring the crosslinking process. These links actlike defects that make the formation of crystalsdifficult during the cooling carried out after thefirst heating of the samples. The exception wasthe mPE1/PP blend, which showed the same val-ues for all irradiation doses. The melting point isrelated to the crystal size, while the crystallinityis related to the total amount of crystallites. Forthis reason, the crystals formed in irradiatedblends present a similar crystal size to thoseformed in the blends without irradiation. Thecrosslinks and branchings act as defect centersthat impede the folding of macromolecular chainsand a reduced crystallinity is observed.29

Although EB irradiation of samples was car-ried out at room temperature, the heat generatedin the sample during the EB irradiation processcould cause a temperature rise that depends onthe specific heat of the material and the EB irra-diation dose. This temperature increment meanssome of the small crystals could be melted. Forthis reason, some of the crosslinks might takeplace during the process within the smallest mol-ten crystals. Consequently, they could hinder thecrystallization during the cooling step. In the pol-yethylene blends this effect is likely to occur,whereas in mPE1/PP these changes were notobserved because of the higher melting tempera-ture of PP.

Figure 2. Influence of EB irradiation on tertiarycarbon ratio (A1).

Figure 3. Influence of EB irradiation on carbonylgroup ratio (A2).



SSA Technique

Evaluation of the miscibility of polymeric blendsby DSC usually points to the presence or absenceof the individual contributions of each componentand changes in melting temperature and/or en-thalpy that could indicate cocrystallization in theevaluated system. Analysis of these parametersby SSA allows us to observe phase segregation.This technique also makes it feasible to analyzein a comprehensive manner the influence of thecrosslinking processes (either by peroxide or irra-diation) on each separate crystalline fraction.30

The SSA technique has been used in the fractio-

nation of ethylene-a-olefin copolymers and their

blends, demonstrating its usefulness to establish

the degree of crystallinity and branch distri-

bution in the blends as well as to evaluate the

miscibility effect on the blends’ crystallinity.23

Figures 4 and 5 show the melting thermo-

grams obtained after an SSA treatment to the

mPE1/HDPE and mPE1/PP blends. These blends

were selected for the SSA analysis because of

the fact that they exhibited relevant behavior in

the previous characterization tests and because

Table 5. Thermal Properties of the Blends at DifferentEB Irradiation Doses (kGy)a

Blend kGy

Temperature, Tm (8C)b Crystallinity, Xc (%)b

Tm1(61) Tm2

(61) Xc1 (61) Xc2 (61)

mPE1/mPE2 0 71 105 22 2250 71 105 14 22

100 73 105 11 21200 70 104 10 17

mPE1/HDPE 0 75 128 23 5250 70 126 21 52

100 70 128 21 51200 70 125 15 43

mPE1/LLDPE 0 75 120 23 3050 71 119 17 31

100 71 118 14 30200 71 118 13 29

mPE1/PP 0 77 164 24 2550 76 162 24 25

100 75 161 23 25200 74 158 23 25

a The melting behavior is after an erased of the thermal history.b The subscripts 1 and 2 mean matrix and dispersed phase, respectively.

Figure 4. SSA heating curves for mPE1/HDPE. Figure 5. SSA heating curves for mPE1/PP.



HDPE and PP represent two very different dis-persed phases. The nonmiscible character of theblends was revealed by a clear separation of themelting zones, with the peaks at lower tempera-tures associated with the less crystalline metallo-cene copolymer used as matrix. The peaks athigher temperatures were assigned to the dis-persed phase. Shakns and Amarasinghe31 foundsimilar results in polyethylene blends with par-tial miscibility by means of a thermal treatmentusing a DSC step crystallization.

The main differences in the mPE1/HDPE andmPE1/PP blends corresponded to the varietyobtained in the thickest lamellae of populationsat higher temperatures induced by the thermaltreatment SSA. A decrease in the crystalline pop-ulations with higher lamellar thickness that cor-respond to HDPE and PP as disperse phase canbe seen in Figures 4 and 5. A decrease in themost perfect lamellar thickness was observed inthe mPE1/HDPE blend and the intensity of thesecondary DSC peak increased with the EB irra-diation dose. A similar variation was also ob-served in the mPE1/PP blend, where the predom-inant effect was a significant reduction of endo-therms at higher temperatures and an increasein endotherms at lower temperatures (especiallyfor 100 and 200 kGy). This effect has been associ-ated with chain-scission reactions in the mostperfect crystalline regions, as has been reportedpreviously in neat PP when it was grafted withpolar monomers.32 Nevertheless, the differencesfound by SSA in this study are related to thechanges induced primarily by the crosslinkingreactions. Chain scission was a comparativelyminor reaction that was observed through gelcontent, MFI, and FTIR.

Although clear evidence of crosslinking reac-tions based on the results of gel content, MFI,and FTIR is present, there exists the possibilitythat some chain-branching reactions were alsoinduced by the irradiation processes. Arnalet al.33 have observed that SSA is very sensitiveto chain branching (more than to the differencesin molecular weight), because it interrupts thelength of the crystallizing chain and producesmolecular fractionation during cooling. Conse-quently, there could be a hindrance in the crys-tallization caused by new links (crosslinking andchain branching) resulting from irradiation.

The crystal size distribution of the matrix wasaltered similar to that of the dispersed phases.The processes of crosslinking and chain branch-ing inhibit the crystallization as the copolymers

cool down from the melt, affecting preferentiallythe longest methylene sequences that form thecrystals of greater size (lamellae).

CONCLUSIONS

Blends prepared using mPE as matrix weretreated using different doses of EB irradiation.Gel content, MFI, and DSC techniques showedthat 100 and 200 kGy EB irradiation doses reachthe highest crosslinking levels. The decrease inmelt flow and solubility (gel content) indicatedthat the incidence of the crosslinking effect washigher than that of the chain branching or scis-sion effects. The decrease in crystallization of pol-ymers (matrix and dispersed phases) showedthat irradiation affects the growth of crystals.These observations were confirmed by the tensileproperties studied, in which the elastic modulusand elastomeric behavior showed dependence onthe EB irradiation doses. Using FTIR-ATR analy-sis an increase in tertiary carbon formation and alow presence of carbonyl groups was observed,confirming the predominance of the crosslinkingreactions over oxidative degradation and chainscission. Using SSA analysis slight changes inlarger crystalline populations have been detectedin mPE1/HDPE and mPE1/PP blends. Thesemodifications are a consequence of chemicalchanges induced in the chain structure by EBirradiation.

The authors gratefully acknowledge the financial sup-port of the Ministerio de Educacion y Ciencia (pro-gram MAT2005-6627-C03) and the European SocialFund (ESF) (‘‘Torres Quevedo’’ Program: PTQ2003-0582). M. A. Cardenas thanks Ms. Carmen Rosalesand Ms. Rosestela Perera for their valuable assistanceduring the blending processes.

REFERENCES AND NOTES

1. Sinn, H.; Kaminsky, W. Adv Organomet Chem1980, 18, 99.

2. Bensason, S.; Minick, J.; Moet, A.; Chum, S.; Hilt-ner, A.; Baer, E. J Polym Sci Part B: Polym Phys1996, 34, 1301.

3. Hseih, E. T.; Tso, C. C.; Byers, J. D.; Johnson,T. W.; Fu, Q.; Cheng, S. Z. Macromol Sci Phys1997, B36, 615.

4. Hussein, I. A. Polym Int 2005, 54, 1330.5. Rana, D.; Lee, C. H.; Cho, K.; Lee, B. H. J Appl

Polym Sci 1998, 69, 2441.



6. Wu, T.; Li, Y.; Zhang, D.-L.; Liao, S.-Q.; Tan,H.-M. J Appl Polym Sci 2004, 91, 905.

7. Rana, D.; Cho, K.; Woo, T.; Lee, B. H.; Choe, S.J Appl Polym Sci 1999, 74, 1169.

8. Peng, Y.; Zhang, Q.; Du, R.; Fu, Q. J Appl PolymSci 2005, 96, 1816.

9. Ho, T.; Martin, J. M. In Metallocene-Based Poly-olefins Preparation, Properties and Technology;Scheirs, J.; Kaminsky, W., Eds.; Wiley: Chichester,2000; Vol. 2, p 175.

10. Aarts, M. W.; Fanichet, L. Polyolefin ElastomersMade with Constrained Geometry Catalysts forthe Rubber Industry; Deutsche Kautschuk Tagung:Stuttgart, 1994.

11. Endstra, W. C. Kaut Gummi Kunstst 1989, 42, 414.12. Miguez-Suarez, J. C.; Biasotto-Mano, E.; Bruno-

Tavares, M. I. J Appl Polym Sci 2000, 78, 899.13. Miguez-Suarez, J. C.; Biasotto-Mano, E.; Chagas-

Bonelii, C. M. Polym Eng Sci 1999, 39, 1398.14. Miguez-Suarez, J. C.; Biasotto-Mano, E. Polym

Degrad Stab 2001, 72, 217.15. Miguez-Suarez, J. C.; Biasotto-Mano, E.; Abra-

hao-Pereira, R. Polym Degrad Stab 2000, 69, 217.16. Miguez-Suarez, J. C.; Biasotto-Mano, E. Polym

Test 2000, 19, 607.17. Tokuda, S.; Kemmotsu, T. Radiat Phys Chem

1995, 46, 905.18. Zaharescu, T.; Setnescu, R.; Jipa, S.; Setnescu, T.

J Appl Polym Sci 2000, 77, 982.19. Clough, R. L. Nucl Instrum Methods Phys Res B

2001, 185, 8.20. Benson, R. S.; Moore, E. A.; Martinez-Pardo, Ma.

E.; Luna, D. Nucl Instrum Methods Phys Res B1999, 151, 174.

21. Mettler Toledo Collected Applications. ThermalAnalysis 2000.

22. Muller, A. J.; Hernandez, Z. H.; Arnal, M. L.;Sanchez, J. J. Polym Bull 1997, 39, 465.

23. Muller, A. J.; Arnal, M. L. Prog Polym Sci 2005,30, 559.

24. Villarreal, N.; Pastor, J. M.; Perera, R.; Rosales,C.; Merino, J. C. Macromol Chem Phys 2002, 203,238.

25. Silverman, J.; Singh, A. Radiation Processing ofPolymer; Oxford University Press: New York,1991; p 6.

26. Clough, R. In Encyclopedia of Polymer Scienceand Engineering; Mark, H.; Bikales, N.; Over-berger, C.; Menges, G., Eds.; Wiley: New York,1988; Vol. 13, p 667.

27. Socrates, G. Infrared and Raman CharacteristicGroup Frequencies. Tables and Charts; Wiley:Chichester, 2001; p 52.

28. Bolland, J. L.; Gee, G. Trans Faraday Soc 1946,42, 244.

29. Khonakdar, H. A.; Morshedian, J.; Mehrabzadeh,M.; Wagenknecht, U.; Jafari, S. H. Eur Polym J2003, 39, 1729.

30. Villarreal, N.; Gobernado-Mitre, I.; Merino, J. C.;Pastor, J. M. In ANTEC Proceedings, Boston,2005.

31. Shakns, R. A.; Amarasinghe, G. Polymer 2000,41, 4579.

32. Villarreal, N.; Pastor, J. M.; Perera, R.; Rosales,C.; Merino, J. C. In ANTEC Procceeding, SanFrancisco, 2002.

33. Arnal, M. L.; Canizales, E.; Muller, A. Polym EngSci 2002, 42, 2048.



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Characterization of electron beam irradiation blends based on metallocene ethylene-1-octene copolymer